Guys, UE4 evolve fast. (@detoxx112, Mightyenigma)
There is now (Since 4.22) a full range of fully supported feature to do this.
No need for external plugins!
There is Spectrum analysis now and envelope followers.
You can drive anything using a .wav file. (and now full MIDI support)
FYI as a good start:
https://forums.unrealengine.com/development-discussion/audio/116874-new-audio-engine-early-access-quick-start-guide?143974-4-16-New-Audio-Engine-Early-Access-Quick-Start-Guide=
This post is originally from 2014 you know
Cheers!